In the field of forestry, the tree or log is subjected to a variety of operations before the final product of dimensioned lumber is obtained. Once the dimensioned lumber has been cut from the log, it is then normally subjected to a drying operation to remove moisture from the lumber. As will be appreciated, a substantial amount of moisture must be removed from the lumber and to do so requires substantial energy input.
Conventionally, the lumber is dried using various wastes from the sawmill and other associated steps as a fuel. Thus, one can use sawdust, wood chips, various pulping wastes, and the like as a source of fuel for heating the air for subsequently drying the lumber.
There are different types of commercially available ovens which are used for such wood drying operations. Normally they utilize a screw conveyor feeding into a combustion chamber wherein air is fed from underneath to the fuel. Such air is known as the primary air and is used for the combustion of the fuel. Subsequently, there may be provided secondary air to assist in the more complete combustion. However, despite the above, it has been found that there is not as complete a combustion as would be desired and therefore, energy is wasted.